1. Field of the Invention
The present invention relates to fluid dynamic-pressure bearing devices for use in hard disk driving devices and hard disk devices incorporating the fluid dynamic-pressure bearing device for rotatably supporting the disk mounting portion.
2. Description of the Related Art
In recent years, miniaturization of personal computers and mounting of hard disks into compact-size portable apparatuses have been advanced. Furthermore, miniaturization of hard disks has been also advanced from a conventional size of 3.5 inch size to more miniaturized sizes such as 2.5 inch and 1.0 inch or less. In view of such trends, there has been a need for miniaturization of fluid dynamic-pressure bearing devices for supporting the hub of a hard disk.
FIG. 11 illustrates a fluid dynamic-pressure bearing which places the hub lower surface on the upper surface of a sleeve such that they face each other with a narrow gap sandwiched therebetween to form a thrust dynamic-pressure bearing and places a tapered sealing portion on the sleeve side surface. With this configuration, the use of a thrust plate can be omitted to reduce the height of the bearing device.
FIG. 12 illustrates a dynamic-pressure bearing device including herringbone shaped thrust dynamic-pressure generating grooves and grooves provided outside thereof for feeding lubricating liquid towards the bearing center. This configuration can prevent the leakage of the lubricating liquid even during high-speed rotation of the bearing.
Although these bearing devices exhibit preferable characteristics, they also suffer certain drawbacks during operation.
With the dynamic-pressure bearing device of FIG. 11, the lubricating liquid can not be circulated between the shaft tip end and the thrust bearing portion, which may induce a significant pressure difference between the shaft tip end portion and the thrust bearing side. With the dynamic-pressure bearing device of FIG. 12, redundant rows of grooves are provided for feeding oil on the thrust dynamic-pressure bearing surface, which prevents sufficient reduction of the resistance during the rotation of the bearing.
FIG. 13 illustrates a dynamic-pressure bearing device which includes a thrust dynamic-pressure bearing portion formed on a sleeve end surface. This device of this example is prone to interruptions of the lubricating liquid outside of the thrust dynamic-pressure bearing portion. In addition, this device is prone to accidental discharge of oil to the outside due to the influence of the rotating hub, which has made it impossible to ensure high reliability.
It is an object of the present invention to realize reliable and small-size fluid dynamic-pressure bearing devices which include a bearing with a small height, induce small shaft losses and are less prone to troubles such as shortage and leakage of lubricating liquid.